This invention relates in general to a method for fabricating a semiconductor device, and more particularly to a method for selectively forming a protective coating on electrically conductive structures within a semiconductor device.
As semiconductor device manufacturers continue to design high performance integrated circuits to meet customer performance demands, a corresponding need for increased signal transmission rates within the device requires the use of electrically conductive materials having low electrical resistance. Those refractory-metals which have a low bulk resistivity have long been considered as materials with potential application for use as a gate electrode, a local interconnect, a capacitor plate or other electrically conductive structure within a semiconductor device. The use of refractory-metals as electrical conductors has been limited because of their lack of compatibility with other materials commonly used in the construction of semiconductor devices. For example, refractory-metals are easily oxidized when exposed to high temperatures commonly encountered in device fabrication. Furthermore, they are susceptible to chemical degradation upon contact with process chemicals used in the fabrication of very-large-scale-integration (VLSI) devices. Additionally, in general passivation materials, such as passivation glasses deposited over conductive leads and transistor gates, do not adhere well to refractory-metals.
In the place of pure refractory-metals, refractory-metal silicides have been commonly used because of their greater degree of compatibility with existing process technology. A disadvantage of the use of refractory-metal silicides in high performance VLSI devices is their inherently high bulk electrical resistivity, 60 to 100 .mu..OMEGA.-cm, versus 6-12 .mu..OMEGA.-cm for selected refractory-metals. The large bulk electrical resistance of refractory-metal silicides does not permit the attainment of high signal transmission rates required by state-of-the-art VLSI devices. Therefore, it would be advantageous if a process could be provided that would permit the application of substantially pure refractory-metals for use as transistor gates, interconnects, capacitor plates, electrical leads and the like.